Tools using go/types sometimes need to implement special handling for
certain errors produced by the type-checker. They can offer suggested
fixes, expand the error position to surrounding syntax, highlight
related syntax (for example in the case of a declaration cycle), link to
additional documentation, group errors by category, or correlate errors
with signals produced by other static analysis tools.
All these require a notion of error identity. Tools need to be able to
reliably determine the nature of an error without re-implementing type
checking logic or parsing error messages. This CL is a first-pass at
adding such an identifier to types.Error: a (for the moment unexported)
field containing one of many declared errorCode constants.
A wide variety of error code constants are defined, and assigned to type
checker errors according to their 'functional equivalence', meaning that
they should be ideally be stable under refactoring.
With few exceptions, each error code is documented with an example that
produces it. This is enforced by tests.
When error codes are exported they will represent quite a large API
surface. For this reason, as well as the likelihood that error codes
will change at the start, both the code field and the codes themselves
are initially unexported. gopls will read these fields using reflection
during this experimental phase. Others can obviously do the same,
provided they accept the lack of forward compatibility.
For #42290
Change-Id: I15e3c2bffd2046c20297b1857057d421f633098a
Reviewed-on: https://go-review.googlesource.com/c/go/+/264179
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>